Recently, research and development are progressing on information recording media (optical disc, such as a BD (Blu-ray Disc (registered trademark), for example) including a plurality of information recording faces. With a plurality of information recording faces, however, distances from the surface on a light source side of the information recording medium to respective information recording faces thereof are different from each other, and therefore, focusing of laser lights on the respective information recording faces through a single objective lens causes spherical aberration due to the difference in distance from the light source side surface to the respective information recording faces of the information recording medium. This makes it difficult to focus the laser lights appropriately on the information recording faces.
In view of the above problem, for example, Japanese Patent Application Laid Open Publication No. 2006-31901 discloses that the angle of divergence of a light incident to the objective lens is changed by driving a beam expander lens, a collimator lens, or the like in the direction of the optical axis to correct the spherical aberration caused due to the difference in distance from the light source side surface to the respective information recording faces of the information recording medium.